The present invention relates to a luminescent display device including a substrate, particularly formed of resin substrate, and a transparent electrode, an auxiliary electrode and a luminescent layer which are laminated on the substrate and also relates to a method of manufacturing such luminescent display device.
Generally, there is known an organic EL (electro-luminescent or electroluminescent) display element, and such organic EL display element has been manufactured on a transparent glass substrate as a luminescent display device.
FIG. 5 represents steps for preparing an organic EL element on a glass substrate. That is, a glass substrate 1 is prepared (step S1). A transparent electrode 2 as anode is formed on the substrate 1 in form of a film (step S2), and in this step S2, the transparent electrode 2 is formed at a high temperature of more than 200xc2x0 C. for the purpose of reducing resistance. This transparent electrode 2 is subjected to a patterning treatment or process by using a photoresist or acid so as to provide a stripe shape.
Next, a metal film 3 constituting an auxiliary electrode is formed on the transparent electrode 2 (step S4). This metal film 3 as auxiliary electrode is then subjected to the patterning treatment, as in the former step S3, by using a photoresist or acid (step S5). In this step S5, although the acid is used for a metal etching treatment, it is important for the acid not to erode the transparent electrode 2. In general, a chlorine-base acid is used for the patterning treatment of the transparent electrode 2 and a mixture acid of phosphoric acid and nitric acid. Such mixture acid is utilized for the etching treatment of Al and Ag alloys, but has a property not eroding the transparent electrode formed at a high temperature, and hence, has been utilized from old days. After the steps mentioned above, a luminescent layer is laminated, and thereafter, a metal electrode as cathode is formed on the luminescent layer in shape of stripe extending in a direction normal to the transparent electrode 2.
When a direct current (DC) field is applied between the transparent electrode (anode side) and the metal electrode (cathode side), an electric current passes an organic compound and the luminescent layer is hence emitted. The light emitted from the luminescent layer is taken out on the transparent electrode side.
In order to make thin an organic EL display device, a resin substrate may be utilized in place of the glass substrate, and in such case, the substrate can be made thin and, in addition, can hardly be cracked. Furthermore, the organic EL display device utilizing the resin substrate has flexibility so as to be bendable, thus being advantageous.
However, in the structure in which, as like as the glass substrate, the transparent electrode and the metal auxiliary electrode are laminated on the substrate, it is obliged for the transparent electrode to be formed at a low temperature less than 100xc2x0 C. because of heat resistant property of the resin substrate. The transparent electrode thus formed at the low temperature has a nature, different from that formed at a high temperature of more than 200xc2x0 C., that is easily eroded by acid. This nature will be also applied to the case of using the mixture acid of phosphoric acid and nitric acid, and the surface of the transparent electrode is corroded and made coarse by such acid at the time of the patterning. On such surface, leak or dark spot is likely generated, which results in inadequate display.
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art described above and to provide a luminescent display device capable of keeping smoothness of a surface of a transparent electrode and obtaining a good displaying result in a case of laminating a transparent electrode and an auxiliary electrode on a resin substrate and also provide a method of manufacturing such luminescent display device.
To achieve the above object and solve the problem raised in the case of preparing the organic EL element on the resin substrate, the inventors of the subject application developed a technology of preparing the organic EL display element on the resin substrate by providing a new layer structure of resin substrate/auxiliary electrode/transparent electrode which is different from the conventional layer structure of glass substrate/transparent electrode/auxiliary electrode.
The above and other objects can be achieved according to the present invention by providing, in one aspect, a luminescent display device comprising:
a resin substrate having one and another surfaces;
an auxiliary electrode made of metal and disposed on the one surface of the resin substrate;
a transparent electrode disposed on the auxiliary electrode, the auxiliary electrode being conductive to the transparent electrode; and
a luminescent layer composed of an organic compound and disposed on the transparent electrode.
According to the above structure, the transparent electrode is formed after the formation and patterning of the metal auxiliary electrode, so that the transparent electrode never be eroded by an etching solution at the time of the patterning to the auxiliary electrode. Therefore, the surface of the transparent electrode can be kept smooth, and moreover, since the metal auxiliary electrode is covered by the transparent electrode, the oxidization of the metal auxiliary electrode can be prevented.
In preferred embodiments of this aspect, a layer of metal oxide is further formed between the resin substrate and the auxiliary electrode.
The metal oxide is formed of a conductive material, which is formed into a film and is then subjected to a patterning treatment or process. The metal oxide is formed of an oxide including at least one of tin (Sn), zinc (Zn) and indium (In).
The metal oxide is formed of an insulating material, which is formed into a film. The metal oxide is formed of an oxide including at least one of aluminum (Al), zirconium (Zr), titanium (Ti), calcium (Ca), magnesium (Mg), chromium (Cr), nickel (Ni) and silicon (Si).
A moisture-proof layer may be further formed between the resin substrate and the metal oxide for preventing any moisture or water content.
According to the above preferred embodiments, the location of the metal oxide layer between the resin substrate and the metal auxiliary electrode can improve the adhesive performance of the auxiliary electrode.
When the metal oxide is formed of a conductive material, there may cause a case where the patterned respective auxiliary electrodes become conductive through the formation of the metal oxide layer below the auxiliary electrode. According to this invention, however, since the metal oxide layer is patterned in the same form as that of the auxiliary electrode, the above defect can be solved. On the other hand, when the metal oxide is formed of an insulating material, the patterned auxiliary electrode does not become conductive even if the metal oxide is disposed below the auxiliary electrode. Thus, the patterning process can be eliminated.
The formation of the moisture-proof layer can shut out the invasion of the moisture or water content to the luminescent layer, thus maintaining the good light emission performance.
The above objects can be also achieved by providing, in another aspect, a method of manufacturing the luminescent display device of the characters mentioned above, comprising the steps of:
preparing a resin substrate having one and another surfaces;
laminating an auxiliary electrode made of metal on the one surface of the resin substrate;
laminating a transparent electrode on the auxiliary electrode, which is conductive to the transparent electrode; and
laminating a luminescent layer composed of an organic compound on the transparent electrode.
In this aspect, a metal oxide may be further formed on the one surface of the resin substrate before the lamination of the auxiliary electrode.
The metal oxide is formed of a conductive material, which is formed in form of film, and is then subjected to a patterning treatment. The metal oxide may be formed of an insulating material, which is formed into a film.
The metal oxide and the auxiliary electrode are patterned at the same time by utilizing a photolithography technology or using an acid. The transparent electrode is formed into a film through sputtering, ion-plating or epitaxial growth treatment or process and then patterned by utilizing a photolithography technology or using an acid.
According to this aspect, substantially the same effects or functions as those mentioned above may be achieved.
Furthermore, it is to be noted that the present invention will be made further clear from the following descriptions made with reference to the accompanying drawings.